The United Mine Workers bargaining council yesterday unanimously approved a highly sweetened tentative contract that could end what is now a 65-day strike against the Bituminous Coal Operators Association.

The 39-member council, with one member absent, acted hours after UMW President Sam Church Jr. and BCOA negotiators approved a proposal that will boost labor costs in the soft-coal industry by about $4.5 million over the next 40 months, the length of the new agreement.

Council members voted to approve this second tentative pact, 36 to 2, then changed the vote on one of unanimous approval in a show of unity. That action, and the apparent upbeat spirit it conveyed, differed from circumstances last March, when the council voted, 21 to 14, to approve the first tentative agreement.

The UMW rank and file rejected the first proposal more than 2 to 1 March 31, prolonging the strike that had begun when the three-year pact expired March 27.

The 160,000 miners affected by the new proposal have several days to study the new proposal. They are scheduled to vote next Saturday, with announcement of the results made a day later.

UMW officials were very optimistic yesterday. "It's a good contract. It's better than the last contract," Church said, referring to the rejected proposal.

Although UMW miners have a well-documented history of unpredictability, Church bases his optimism on:

The rejected agreement allowed the BCOA's 130 member firms to discontinue royalty payments of $1.90 per ton to the UMW's health and welfare funds. The payments effectively constitute a UMW tax on supplemental coal that BCOA co mpanies purchased from mines not covered by BCOA/UMW agreements.

The union's rank and file bitterly opposed ending the payments on grounds that it could spur increased purchases of non-union coal. The new contract not only reinstitutes the provisio;n, but also increases royalty payments to $2.23 per ton in the third year of the contract, with substantial increases in the first two years of the agreement.

The rejected agreement contained a "scope and coverage" clause that read: "Where contracting out is permitted . . . prior custom and practice [of using UMW workers on the subcontracting jobs] shall not be construed to limit in any way the employers' choice of contractors."

UMW members saw that as a serious threat to their jobs and union security because, in their view, it allowed potential widespread use of nonunion labor in mine repair and other subcontracting work.

New contract language stipulates that BCOA firms use nonunion subcontractors only when their active workers, nearly all of them UMW members, or their laid-off employes, most of whom are union members, are not available.

Although the economic package was not a major issue in rejection of the first proposal, which offered a 35.6 percent increase in wages and benefits, the union now has won a compensation package of 37.5 percent -- spread over 40 months, as opposed to the first pact's 36 months.

The average pay of underground miners, currently about $23,500 annually, would increase to nearly $33,000 annually in the third year of the new agreement, according to union officials.

The rejected agreement contained no back-to-work bonus, largely because neither union nor industry negotiators anticipated another lengthy UMW walkout. The new agreement promises a $150, one-time bonus to miners on the job the first day work resumes.The bonus was given in lieu of a strike insurance plan sought by the union.

Usually reticent BCOA officials yesterday continued their policy of not commenting on specific contract items. However, BCOA chief negotiator B. R. (Bobby) Brown told reporters: "We've addressed most of the issues. . . . It's a good contract for the union."